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Insect control can be pesky

Here's one for the "Facts You Never Thought You'd Need to Know" file:

A bottlecap can hold enough water to hatch mosquitoes.

In the age of West Nile virus, acting on that bit of seeming trivia could spell the difference between sickness and health.

Because of the threat of West Nile virus, which can cripple and kill, the public has developed a keen interest in - and some confusion over - what kinds of water basins might produce the disease-carrying bugs.

When it comes to harboring enough water for mosquitoes to thrive, it's easy to find fault.

Even diligent water-watchers such as Carolyn Hopkins wonder if they're unwittingly part of the problem.

In the front yard of her Greenhaven home, Hopkins has a fountain with a broken pump. She cleans it every week or two and adds a teaspoon of powdered chlorine, hoping the chemical will deter mosquitoes from laying eggs in the water.

A couple of weeks ago, a neighbor said, "Oh, you'd better get that water drained."

Should she? Hopkins wondered. "I'd rather have water in it than have it be empty and gather dirt and leaves," she said.

Local mosquito control officials say these sorts of questions are popping up regularly, and the answers aren't necessarily obvious.

Chlorine, for example, isn't a good solution, they say.

For one thing, it's not particularly effective.

"The chlorine probably won't kill the mosquitoes unless you put in an awful lot," said Jamesina Scott, a vector ecologist at the Placer Mosquito Abatement District.

For another thing, the chemical can be hazardous in the wrong places and in high levels.

Dave Brown, general manager of the Sacramento-Yolo Mosquito and Vector Control District, warns against the undiscriminating use of chlorine.

"I'm worried about (someone thinking), 'Oh, my dog dish, I'll put chlorine in that,' " he said.

In fact, it's not chlorine itself that keeps mosquitoes from laying eggs in swimming pools.

Scott said chlorine won't kill mosquitoes in the concentrations typically used in pools. What chlorine does is prevent the growth of algae that mosquitoes feed on.

To understand what kinds of water containers attract mosquitoes, it's helpful to know a bit about mosquito biology.

Before they become flying adults, mosquitoes live in water. The ideal nursery, from a mother mosquito's point of view, is standing water filled with algae, bacteria, and detritus such as leaf litter upon which the juvenile mosquitoes can feed.

"It doesn't take a lot of water," said Scott, who has found mosquito eggs floating in the few drops that collected in an upturned bottlecap.

Mosquitoes lay "rafts" of eggs, up to 400 at a time. One raft is only about a quarter-inch long, resembling a speck of soot.

Larvae emerge from the eggs and hang at the surface of the water - head down, tail up. They poke a siphon out to breathe, while they eat stuff in the water.

Larval mosquitoes shed their skin four times as they grow, then become pupae, a stage in which they encase themselves - roughly like caterpillars turning into butterflies - to emerge as adults with wings.

In warm weather, mosquitoes can go from egg to adult in less than a week.

Ridding property of mosquito habitat takes a careful eye.

"You'd be surprised, if you start walking around in people's backyards - which often look different from people's front yards - the junk (you see)," said Tom Scott, an entomologist at the University of California, Davis. "It doesn't look like junk to them, but the stuff can accumulate."

The list of possible culprits is long and varied. A toy dump truck that catches water from a sprinkler. Plastic cups left out from the party the weekend before. Saucers under potted plants. Children's swimming pools.

Unnecessary containers should be emptied. Containers meant to hold water, such as pet bowls or bird baths, should be cleaned and freshened daily.

As for fountains with broken pumps?

Scott recommends a product called a Mosquito Dunk. It's an object shaped like a doughnut that releases a bacterial toxin lethal to mosquito larvae, but non-toxic to birds or pets.

Another option for decorative water basins is mosquito fish. Both the Placer Mosquito Abatement District and Sacramento-Yolo Mosquito and Vector Control District give mosquito-eating fish free to district residents.

The little gray guppies grow to less than 3 inches in length and reproduce easily, providing continuous control of mosquito larvae, Scott said.

The districts even put mosquito fish into unused, unmaintained swimming pools. Brown said "green pools" - green with algae - may be one of the region's hardest-to-solve mosquito problems.

That's because mosquito-control workers can't easily locate or reach them.

"I can see wetlands, I can see the roadside ditches, I can see the rice fields, but I can't see into your backyards," Brown said.

During a recent aerial survey over Citrus Heights, Brown said the district counted more than 100 unmaintained pools in a 4-square-mile area. He estimates there are thousands throughout Sacramento and Yolo counties.

Brown said the district is hopeful that people with green pools would allow district workers onto their properties to make the pools inhospitable to mosquitoes, but if they don't, the district may go to court to get authority to enter private properties.

"If you've got a problem with a pool right now, please call us and we'll address the mosquitoes," Brown said.

"We won't take care of the pool," he added, noting that some folks have asked if the district would get their pools up and running again. "But we won't charge to take care of the mosquitoes."


To learn how to obtain free mosquito fish, or for answers to questions about how to prevent mosquitoes from breeding in your neighborhood, call:

* Sacramento-Yolo Mosquito and Vector Control District: (916) 685-1022 or (800) 429-1022.

* Placer Mosquito Abatement District: (916) 435-2140.

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